Projection display device, display control method, and display control program

ABSTRACT

A projection display device includes: a light modulation unit that spatially modulates, in accordance with image data that has been input, light emitted by a light source; a projection optical system that projects the light that has been spatially modulated onto a projection surface of a vehicle; a measurement information acquisition unit that acquires measurement information measured by an information measuring device; an image display control unit that performs either first display control or second display control as defined herein; and a warning determination unit that determines, in accordance with the measurement information, whether or not a warning is necessary, and the image display control unit performs the second display control when the warning determination unit determines that the warning is necessary, and performs the first display control when the warning determination unit determines that the warning is not necessary.

CROSS REFERENCE TO RELATED APPLICATION

This is a continuation of International Application No.PCT/JP2017/017171 filed on May 1, 2017, and claims priority fromJapanese Patent Application No. 2016-181516 filed on Sep. 16, 2016, theentire disclosures of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a projection display device, a displaycontrol method, and a computer readable medium storing a display controlprogram.

2. Description of the Related Art

A head-up display (HUD) for a vehicle has been known. In the HUD, acombiner that is disposed on a windshield of a vehicle, such as anautomobile, a train, a ship, a heavy machine, an aircraft, or anagricultural machine, or that is disposed near a position before thewindshield is used as a screen, and light is projected onto the screento display an image. The HUD enables a driver to visually recognize animage that is based on light projected from the HUD as a real image onthe screen or as a virtual image in front of the screen.

Systems for assisting driving by using the HUD are described inJP2015-197706A, JP2015-225615A, JP2016-112987A, JP2013-535376A, andJP2006-058064A.

JP2015-197706A and JP2015-225615A describe an HUD that controls adisplayed image in accordance with information from a control unit of anautomobile.

JP2016-112987A, JP2013-535376A, and JP2006-058064A describe an HUD thatacquires information of various types of sensors mounted in anautomobile and controls a displayed image in accordance with theinformation.

SUMMARY OF THE INVENTION

In recent years, automated driving of vehicles has been developed towardpractical use, but there is an issue that automated driving or the likeincreases a burden on a control unit of an automobile. That is, when theHUD controls a displayed image in accordance with information from thecontrol unit of the automobile, as in JP2015-197706A and JP2015-225615A,a delay in display is likely to occur when the control unit of theautomobile is highly loaded.

As in JP2016-112987A, JP2013-535376A, and JP2006-058064A, when the HUDconstantly performs a process of information from various types ofsensors and generation of image data based on this process, the HUD ishighly loaded, and an increase in temperature inside the HUD and a delayin display are likely to occur. For example, when a delay occurs indisplaying warning information for notifying a driver of a situationwhere danger is approaching, a delay is likely to occur in an action foravoiding the danger.

The present invention has been made in view of the above-describedcircumstances, and an object of the present invention is to provide aprojection display device, a display control method, and a displaycontrol program that are capable of assisting safe driving whilepreventing a delay in displaying important information.

A projection display device of the present invention includes: a lightmodulation unit that spatially modulates, in accordance with image datathat has been input, light emitted by a light source; a projectionoptical system that projects the light that has been spatially modulatedonto a projection surface of a vehicle; a measurement informationacquisition unit that acquires measurement information measured by aninformation measuring device; an image display control unit thatperforms either first display control for generating image data inaccordance with information received from a control unit that controlsthe vehicle and for inputting the image data to the light modulationunit or second display control for generating image data in accordancewith the measurement information and for inputting the image data to thelight modulation unit; and a warning determination unit that determines,in accordance with the measurement information, whether or not a warningis necessary, wherein the image display control unit performs the seconddisplay control when the warning determination unit determines that thewarning is necessary, and performs the first display control when thewarning determination unit determines that the warning is not necessary.

A display control method for a projection display device of the presentinvention is a display control method for a projection display devicehaving a light modulation unit that spatially modulates, in accordancewith image data that has been input, light emitted by a light source,and a projection optical system that projects the light that has beenspatially modulated onto a projection surface of a vehicle, the displaycontrol method including: a measurement information acquisition step ofacquiring measurement information measured by an information measuringdevice mounted in the vehicle; an image display control step ofperforming either first display control for generating image data inaccordance with information received from a control unit that controlsthe vehicle and for inputting the image data to the light modulationunit or second display control for generating image data in accordancewith the measurement information and for inputting the image data to thelight modulation unit; and a warning determination step of determining,in accordance with the measurement information, whether or not a warningis necessary, wherein the image display control step performs the seconddisplay control when the warning determination step determines that thewarning is necessary, and performs the first display control when thewarning determination step determines that the warning is not necessary.

A display control program for a projection display device of the presentinvention is a display control program for a projection display devicehaving a light modulation unit that spatially modulates, in accordancewith image data that has been input, light emitted by a light source,and a projection optical system that projects the light that has beenspatially modulated onto a projection surface of a vehicle, the displaycontrol program causing a computer to execute: a measurement informationacquisition step of acquiring measurement information measured by aninformation measuring device mounted in the vehicle; an image displaycontrol step of performing either first display control for generatingimage data in accordance with information received from a control unitthat controls the vehicle and for inputting the image data to the lightmodulation unit or second display control for generating image data inaccordance with the measurement information and for inputting the imagedata to the light modulation unit; and a warning determination step ofdetermining, in accordance with the measurement information, whether ornot a warning is necessary, wherein the image display control stepperforms the second display control when the warning determination stepdetermines that the warning is necessary, and performs the first displaycontrol when the warning determination step determines that the warningis not necessary.

According to the present invention, it is possible to provide aprojection display device, a display control method, and a displaycontrol program that are capable of assisting safe driving whilepreventing a delay in displaying important information.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram illustrating an indoor configuration of anautomobile 10 in which an HUD 100, which is an embodiment of aprojection display device of the present invention, is mounted;

FIG. 2 is a schematic diagram illustrating internal hardwareconfigurations of a control unit 4 of the HUD 100 and the automobile 10illustrated in FIG. 1;

FIG. 3 is a functional block diagram of a system control unit 60illustrated in FIG. 2;

FIG. 4 is a flowchart for describing an operation of the HUD 100illustrated in FIG. 1;

FIG. 5 is a diagram illustrating an example of an image displayed by theHUD 100;

FIG. 6 is a diagram illustrating another example of an image displayedby the HUD 100; and

FIG. 7 is a diagram illustrating still another example of an imagedisplayed by the HUD 100.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, an embodiment of the present invention will be describedwith reference to the drawings.

FIG. 1 is a schematic diagram illustrating an indoor configuration of anautomobile 10 in which a head-up display (HUD) 100, which is anembodiment of a projection display device of the present invention, ismounted.

A part of a front windshield 1 of the automobile 10 is a region that hasbeen processed to reflect image light, which will be described below,and this region constitutes a projection surface 2.

An imaging device 9 attached to a rearview mirror 8 is used to capturean image of the inside of the automobile 10 and is connected to a systemcontrol unit 60 (described below) of the HUD 100 in a wired or wirelessmanner. A captured image signal acquired through image capturing by theimaging device 9 is transferred to the system control unit 60 of the HUD100 by wired communication or wireless communication.

The HUD 100 is mounted in the automobile 10 and enables a driver of theautomobile 10 to visually recognize a virtual image or real image byusing image light projected onto the projection surface 2, which is aregion of a part of the front windshield 1 of the automobile 10.

The HUD 100 may be used by being mounted in a vehicle, such as a train,a heavy machine, a construction machine, an aircraft, a ship, or anagricultural machine, as well as an automobile.

In the example illustrated in FIG. 1, the HUD 100 is built in adashboard 3 of the automobile 10. The dashboard 3 is a member thatcontains, in its inside, built-in components including gauges forpresenting information necessary for driving, such as a speedometer, atachometer, a fuel gauge, a water temperature gauge, an odometer, or thelike of the automobile 10.

The HUD 100 includes a control unit 4, a diffusion member 5, areflection mirror 6, and a concave mirror 7. The control unit 4 includesa light source and a light modulation element that spatially modulates,in accordance with image data, light emitted by the light source. Thediffusion member 5, the reflection mirror 6, and the concave mirror 7constitute a projection optical system that projects, onto theprojection surface 2 of the front windshield 1, image light that hasbeen spatially modulated by the light modulation element of the controlunit 4.

The diffusion member 5 is a member that diffuses the image light thathas been spatially modulated by the light modulation element of thecontrol unit 4, thereby making a plane light source. As the diffusionmember 5, a micromirror array having a fine structure on its surface, adiffusion mirror, a reflection holographic diffuser, or the like isused.

The reflection mirror 6 reflects the image light diffused by thediffusion member 5.

The concave mirror 7 enlarges and reflects the image light reflected bythe reflection mirror 6 and projects the image light onto the projectionsurface 2. The projection surface 2 of the front windshield 1 has beenprocessed to reflect the image light projected from the concave mirror 7in the direction of the eyes of the driver.

Alternatively, the HUD 100 may be disposed near the ceiling of theautomobile 10, for example, and may have a configuration of projectingimage light onto a combiner of a sun visor type installed near theceiling of the automobile 10. In this configuration, the combinerconstitutes a projection surface.

The driver of the automobile 10 is able to visually recognizeinformation, such as an icon or characters, for assisting driving, bylooking at a virtual image that is based on the image light projectedonto and reflected by the projection surface 2. In addition, theprojection surface 2 has a function of allowing light from the outside(outside world) of the front windshield 1 to pass therethrough. Thus,the driver is able to visually recognize an image in which a virtualimage that is based on the image light projected from the concave mirror7 and an outside view are superimposed on one another.

FIG. 2 is a schematic diagram illustrating internal hardwareconfigurations of the control unit 4 of the HUD 100 and the automobile10 illustrated in FIG. 1.

The control unit 4 includes a light source unit 40, a light modulationelement 44, a driving unit 45 that drives the light modulation element44, a motion sensor 50, and a system control unit 60 that centrallycontrols the entire HUD 100.

The system control unit 60 includes one or more of various types ofprocessors, a read only memory (ROM) storing a program or the likeexecuted by the processors, and a random access memory (RAM) functioningas a work memory of the processors.

The various types of processors include a central processing unit (CPU),which is a general-purpose processor that executes a program to performvarious types of processes; a programmable logic device (PLD), which isa processor capable of changing the circuit configuration aftermanufacturing, such as a field programmable gate array (FPGA); or adedicated electric circuit or the like, which is a processor having acircuit configuration designed specifically to execute a specificprocess, such as an application specific integrated circuit (ASIC).

The structure of these various types of processors is, morespecifically, an electric circuit in which circuit elements such assemiconductor elements are combined.

The system control unit 60 may be constituted by one of the varioustypes of processors or may be constituted by a combination of two ormore processors of the same type or different types (for example, acombination of a plurality of FPGAs or a combination of a CPU and anFPGA).

The light source unit 40 includes a light source control unit 40A, an Rlight source 41 r serving as a red light source that emits red light, aG light source 41 g serving as a green light source that emits greenlight, a B light source 41 b serving as a blue light source that emitsblue light, a dichroic prism 43, a collimator lens 42 r provided betweenthe R light source 41 r and the dichroic prism 43, a collimator lens 42g provided between the G light source 41 g and the dichroic prism 43,and a collimator lens 42 b provided between the B light source 41 b andthe dichroic prism 43. The R light source 41 r, the G light source 41 g,and the B light source 41 b constitute a light source of the HUD 100.

The dichroic prism 43 is an optical member for guiding rays of lightemitted by the R light source 41 r, the G light source 41 g, and the Blight source 41 b to an identical light path. The dichroic prism 43allows red light collimated by the collimator lens 42 r to passtherethrough and emits the red light to the light modulation element 44.In addition, the dichroic prism 43 allows green light collimated by thecollimator lens 42 g to be reflected thereby and emits the green lightto the light modulation element 44. Furthermore, the dichroic prism 43allows blue light collimated by the collimator lens 42 b to be reflectedthereby and emits the blue light to the light modulation element 44. Theoptical member having such a function is not limited to the dichroicprism. For example, a cross dichroic mirror may be used.

A light emitting element, such as a laser or a light emitting diode(LED), is used as each of the R light source 41 r, the G light source 41g, and the B light source 41 b. The light source of the HUD 100 is notlimited to the three light sources, that is, the R light source 41 r,the G light source 41 g, and the B light source 41 b, and may beconstituted by one light source, two light sources, or four or morelight sources.

The light source control unit 40A controls each of the R light source 41r, the G light source 41 g, and the B light source 41 b, and performscontrol to cause light to be emitted by each of the R light source 41 r,the G light source 41 g, and the B light source 41 b.

The light modulation element 44 spatially modulates, in accordance withimage data received from the system control unit 60, the rays of lightemitted by the R light source 41 r, the G light source 41 g, and the Blight source 41 b and emitted from the dichroic prism 43.

As the light modulation element 44, for example, liquid crystal onsilicon (LCOS), a digital micromirror device (DMD), a micro electromechanical systems (MEMS) element, a liquid crystal display element, orthe like may be used.

The driving unit 45 drives the light modulation element 44 in accordancewith image data received from the system control unit 60 and causesimage light that has been spatially modulated in accordance with theimage data (red image light, blue image light, and green image light) tobe emitted from the light modulation element 44 to the diffusion member5. The light modulation element 44 and the driving unit 45 constitute alight modulation unit of the HUD 100.

The projection optical system constituted by the diffusion member 5, thereflection mirror 6, and the concave mirror 7 illustrated in FIG. 1 isoptically designed so that an image that is based on image lightprojected onto the projection surface 2 can be visually recognized bythe driver as a virtual image at a position in front of the frontwindshield 1. The projection optical system may be optically designed sothat the image that is based on the image light can be visuallyrecognized by the driver as a real image on the front windshield 1.

The motion sensor 50 is an information measuring device that measuresinformation about a motion of the HUD 100 relative to a ground surface.The motion sensor 50 is constituted by, for example, one or both of anacceleration sensor that measures an acceleration generated in the HUD100 and an angular rate sensor that measures an angular rate generatedin the HUD 100.

Measurement information measured by the motion sensor 50 is input to thesystem control unit 60. Hereinafter, a description will be given underthe assumption that the motion sensor 50 includes an acceleration sensorand an angular rate sensor.

The system control unit 60 controls the light source control unit 40Aand the driving unit 45 to cause image light that is based on image datato be emitted from the control unit 4 to the diffusion member 5, inaccordance with an instruction from a control unit 70 of the automobile10.

The automobile 10 includes the control unit 70 that centrally controlsthe entire automobile 10, a steering control unit 71 that controls asteering, an acceleration/deceleration control unit 72 that controlsacceleration/deceleration of the automobile 10 by controlling a brakeand an accelerator, a display unit 73, a navigation device 74, an enginecontrol unit 75 that controls an engine of the automobile 10 in responseto an instruction from the control unit 70, a motion sensor 76, a radar77, and the imaging device 9.

The control unit 70 includes one or more of the above-described varioustypes of processors, a ROM storing a program or the like executed by theprocessors, and a RAM functioning as a work memory of the processors.

The automobile 10 is settable to a first mode (automated driving mode)in which driving is performed in accordance with an instructioninternally generated by the control unit 70 or an instruction externallyand wirelessly received by the control unit 70, and a second mode(manual driving mode) in which a person drives manually.

When the first mode is set, the processor of the control unit 70 inputsan internally generated instruction or an externally and wirelesslyreceived instruction to the steering control unit 71 and theacceleration/deceleration control unit 72.

In accordance with the instruction from the control unit 70, thesteering control unit 71 controls the steering to control the directionin which the automobile 10 drives.

In accordance with the instruction from the control unit 70, theacceleration/deceleration control unit 72 controls the brake and theaccelerator to control the running speed of the automobile 10.

When the second mode is set, the control unit 70 does not generate theabove-described instruction and does not control the steering controlunit 71 and the acceleration/deceleration control unit 72. Thus, in thefirst mode, the processing load on the control unit 70 is relativelyhigh.

The motion sensor 76 is an information measuring device for measuring amotion of the automobile 10 relative to the ground surface, and isconstituted by, for example, one or both of an acceleration sensor andan angular rate sensor. The measurement information measured by themotion sensor 76 is input to the navigation device 74.

The radar 77 is an information measuring device for recognizing anobstacle or measuring a distance to the obstacle, and is, for example, alaser radar, an ultrasonic radar, a millimeter-wave radar, or the like.

Although not illustrated, the automobile 10 includes, mounted therein,another information measuring device for measuring a state of theautomobile 10 or surroundings of the automobile 10.

Another information measuring device mounted in the automobile 10 may bean illuminance sensor for detecting ambient illuminance, a gauge (atachometer, a speedometer, a cooling water temperature gauge, a fuelgauge, or the like), a Global Positioning System (GPS) receiver formeasuring position information, or the like.

The display unit 73 is a liquid crystal display device or the like builtin, for example, a center console between a driver's seat and apassenger seat, and displays various pieces of information in accordancewith an instruction from the control unit 70.

The navigation device 74 generates route guidance information forperforming route guidance to a destination, in accordance withmeasurement information measured by the motion sensor 76, positioninformation measured by the GPS receiver, running speed informationmeasured by the speedometer of the automobile 10, and the like, andinputs the generated route guidance information to the control unit 70.

The imaging device 9 captures an image of a subject by using an opticalsystem and an imaging element, and inputs a captured image signalacquired through the image capturing to the system control unit 60 ofthe HUD 100. The imaging device 9 captures, for example, an image of arange including the face of a person seated on the driver's seat of theautomobile 10.

The imaging device 9 captures an image of the driver to acquireinformation indicating a state of the driver, and is one of informationmeasuring devices.

The measurement information measured by a device, other than the imagingdevice 9 and the motion sensor 76, among the information measuringdevices mounted in the automobile 10, is input to the control unit 70.The measurement information measured by the speedometer, the radar 77,and the imaging device 9 among the information measuring devices mountedin the automobile 10 is also input to the system control unit 60 of theHUD 100.

The measurement information measured by the speedometer, the radar 77,and the imaging device 9 is preferably input to the system control unit60 without passing through the control unit 70.

The ROM of the control unit 70 stores, in advance, display items thatcan be displayed by the HUD 100.

The control unit 70 acquires the measurement information measured by theinformation measuring devices mounted in the automobile 10, the routeguidance information generated by the navigation device 74, and thelike. In accordance with these pieces of information, the control unit70 decides necessary information among the foregoing display items asdisplay target information that is to be displayed by the HUD 100, andinputs the display target information to the system control unit 60 ofthe HUD 100.

The following (1) to (4) are examples of display items that can bedisplayed by the HUD 100, but the display items are not limited thereto.

(1) Information indicating an operation state of the automobile 10, suchas speed information, engine revolutions per minute (RPM) information,engine cooling water temperature information, remaining fuelinformation, real-time fuel efficiency information, direction indicatorblink information, or headlight lighting direction information of theautomobile 10; (2) Information indicating that the automobile 10 needsmaintenance, such as information indicating that a brake pad is worn,information indicating that the level of engine oil has decreased, orinformation indicating that the temperature of engine cooling water ishigh; (3) Route guidance information generated by the navigation device74; and (4) Information indicating danger involved in driving, such asinformation indicating the presence and position of an obstacle, such asanother vehicle or another person, or information indicating that theautomobile 10 is approaching an obstacle.

FIG. 3 is a functional block diagram of the system control unit 60illustrated in FIG. 2.

The system control unit 60 includes a measurement informationacquisition unit 61, a warning determination unit 62, and an imagedisplay control unit 63. The measurement information acquisition unit61, the warning determination unit 62, and the image display controlunit 63 are configured by executing a program stored in the ROM by theprocessor of the system control unit 60. The program includes a displaycontrol program.

The measurement information acquisition unit 61 acquires pieces ofinformation measured by one or more of the information measuring devicesmounted in the automobile 10 and by the motion sensor 50 serving as aninformation measuring device mounted in the HUD 100.

The warning determination unit 62 determines, in accordance with any ofthe pieces of information acquired by the measurement informationacquisition unit 61, whether or not a warning to the driver isnecessary. Here, a warning means giving a notification indicating that acertain action needs to be taken to avoid danger.

Hereinafter, examples of a case where the warning determination unit 62determines that a warning is necessary will be given, but the case isnot limited to thereto.

(A) When the running speed information acquired from the speedometer isgreater than or equal to a speed threshold value that is set in advance,the warning determination unit 62 determines that a notificationprompting speed reduction is necessary.

(B) When the engine RPM acquired from the gauge is greater than or equalto an RPM threshold value that is set in advance, the warningdetermination unit 62 determines that a notification prompting adecrease in the force of stepping on the accelerator is necessary.

(C) When the acceleration information acquired from the motion sensor 50is greater than or equal to an acceleration threshold value that is setin advance, the warning determination unit 62 determines that anotification prompting speed reduction is necessary.

(D) When the acceleration information acquired from the motion sensor 50suddenly changes to the threshold value or smaller, the warningdetermination unit 62 determines that there is a risk of collision withan obstacle, and determines that a notification prompting the driver totake a defensive posture (for example, a posture in which the driver'shead is in the driver's hands, with the head kept down) is necessary.

(E) When the amount of motion of the automobile 10 in the right-hand andleft-hand directions based on the angular rate information acquired fromthe motion sensor 50 is greater than or equal to a motion thresholdvalue over a predetermined period, the warning determination unit 62determines that the driver is feeling sleepy and is driving in a zig zagmanner, and determines that a notification prompting awakening isnecessary to stop the zig-zag driving.

(F) The warning determination unit 62 performs predetermined imageprocessing on a captured image signal acquired from the imaging device 9to measure the number of blinks of a person seated on the driver's seat.When the value of the number of blinks in a predetermined period isgreater than or equal to a number-of-times threshold value, the warningdetermination unit 62 determines that the driver is feeling sleepy anddetermines that a notification prompting awakening is necessary.

(G) The warning determination unit 62 calculates the distance betweenthe automobile 10 and an obstacle in accordance with the measurementinformation acquired from the radar 77. When the distance is smallerthan or equal to a distance threshold value that is set in advance, thewarning determination unit 62 determines that there is a risk ofcollision with the obstacle, and determines that a notificationprompting the driver to take a defensive posture is necessary.

The ROM of the system control unit 60 stores the content (for example,the notifications described in the foregoing (A) to (G)) of warnings(notifications indicating that a certain action is necessary) that aredetermined to be necessary by the warning determination unit 62, inassociation with warning information.

As a result of determination by the warning determination unit 62, whenit is determined that a warning is not necessary, the image displaycontrol unit 63 performs first display control for generating, inaccordance with display target information received from the controlunit 70, first image data for displaying the display target informationin a predetermined layout, and for inputting the first image data to thedriving unit 45.

The first image data is, for example, image data for displaying at leastone of the pieces of information included in the foregoing display items(1) to (4).

As a result of determination by the warning determination unit 62, whenit is determined that a warning is necessary, the image display controlunit 63 performs second display control for retrieving, from the ROM,warning information corresponding to the content of the warning that hasbeen determined to be necessary, for generating second image data fordisplaying the warning information in a predetermined layout, and forinputting the second image data to the driving unit 45.

The second image data is image data corresponding to the content of thewarning that has been determined to be necessary by the warningdetermination unit 62. The content of the warning is decided inaccordance with the information acquired by the measurement informationacquisition unit 61, as described in the foregoing (A) to (G) asexamples. Thus, the second image data is image data that is based on theinformation acquired by the measurement information acquisition unit 61.

FIG. 4 is a flowchart for describing an operation of the HUD 100illustrated in FIG. 1. The process illustrated in FIG. 4 is repeatedlyperformed while the power of the HUD 100 is in an ON state.

Upon the power of the HUD 100 being turned on, the control unit 70 ofthe automobile 10 repeatedly performs a process of determining thecontent to be displayed on the HUD 100 in accordance with various piecesof information measured by the information measuring devices mounted inthe automobile 10, information received from the navigation device 74,and the like, and inputting display target information to the systemcontrol unit 60 of the HUD 100.

On the other hand, upon the power being turned on, the measurementinformation acquisition unit 61 of the HUD 100 acquires measurementinformation measured by one or more of the information measuring devicesof the automobile 10 and by the motion sensor 50 (step S1).Subsequently, the warning determination unit 62 determines, inaccordance with the measurement information acquired by the measurementinformation acquisition unit 61, whether or not a warning is necessary(step S2).

When it is determined that a warning is not necessary (NO in step S2),the image display control unit 63 generates first image data inaccordance with the display target information that has been receivedfrom the control unit 70, and inputs the first image data to the drivingunit 45 (step S3).

The driving unit 45 drives the light modulation element 44 in accordancewith the first image data received from the image display control unit63, thereby projecting image light that is based on the first image dataonto the projection surface 2 (step S4). Accordingly, as illustrated inFIG. 5 as an example, an image 81 including route guidance information,an estimated time of arrival at the destination, and running speedinformation is projected onto the projection surface 2 and is observedby the driver.

On the other hand, when it is determined that a warning is necessary(YES in step S2), the image display control unit 63 retrieves, from theROM, warning information corresponding to the content of the warningdetermined to be necessary, generates second image data for displayingthe retrieved warning information, and inputs the second image data tothe driving unit 45 (step S5). Step S3 and step S5 constitute an imagedisplay control step.

The driving unit 45 drives the light modulation element 44 in accordancewith the second image data received from the image display control unit63, thereby projecting image light that is based on the second imagedata onto the projection surface 2 (step S6).

For example, when the content of the warning is the content shown in theforegoing (A) or (C), an image 82 prompting speed reduction by pressingof the brake is projected onto the projection surface 2, as illustratedin FIG. 6, and is observed by the driver.

Alternatively, when the content of the warning is the content shown inthe foregoing (F), an image 83 of an alarm clock prompting awakening isprojected onto the projection surface 2, as illustrated in FIG. 7, andis observed by the driver. The image 83 may be displayed at a luminancehigher than the luminance of an image projected onto the projectionsurface 2 in accordance with the first image data, or may be displayedwhile being blinked.

As described above, according to the HUD 100, it is possible todetermine whether or not a warning is necessary, in accordance withpieces of information measured by one or more of the informationmeasuring devices mounted in the automobile 10 and by the motion sensor50 serving as an information measuring device mounted in the HUD 100,without using information received from the control unit 70 of theautomobile 10. Thus, even in a situation where the processing load onthe control unit 70 of the automobile 10 is high, the image illustratedin FIG. 6 or 7 for giving a warning can be displayed without delay, andsafe driving can be assisted.

For example, when the automobile 10 is in the first mode, the processingload on the control unit 70 of the automobile 10 may increase. Even insuch a case, with the HUD 100, the system control unit 60 is able toinstantaneously determine an emergency and to present an appropriatewarning with a minimized display delay.

In addition, the HUD 100 includes the motion sensor 50, which is aninformation measuring device. Thus, the system control unit 60 of theHUD 100 is able to acquire information from the motion sensor 50 morequickly than from another information measuring device. Thus, the systemcontrol unit 60 is able to quickly determine whether or not a warning ofthe content shown in the foregoing (C), (D), or (E) is necessary,further shorten a display delay time, and assist more safe driving.

In the description given above, measurement information is also input tothe system control unit 60 from one or more of the information measuringdevices mounted in the automobile 10, but this is not essential.

The system control unit 60 of the HUD 100 may acquire only themeasurement information measured by the motion sensor 50 and determine,in accordance with the measurement information, whether or not a warningis necessary. Also with this configuration, it is possible toindependently determine whether or not a warning of the content shown inthe foregoing (C), (D), or (E) is necessary and quickly give thewarning.

In the configuration in FIG. 2, the motion sensor 50 of the HUD 100 maybe omitted, and the measurement information measured by the motionsensor 76 of the automobile 10 may be input to the system control unit60. With this configuration, the configuration of the HUD 100 can besimplified and the manufacturing cost can be reduced.

In addition, in the configuration in FIG. 2, the motion sensor 50 of theHUD 100 may be omitted, and the measurement information measured by atleast one of the information measuring devices mounted in the automobile10 may be input to the system control unit 60. With this configuration,the configuration of the HUD 100 can be simplified and the manufacturingcost can be reduced.

Preferably, the image display control unit 63 of the HUD 100 isconfigured to selectively perform the first display control or thesecond display control only when the first mode is set, and to performonly the first display control (display of an image according to aninstruction from the control unit 70 of the automobile 10) when thesecond mode is set.

With this configuration, in the second mode in which the processing loadon the control unit 70 of the automobile 10 is low, the processing loadon the system control unit 60 of the HUD 100 can be reduced. Thus, anincrease in temperature inside the HUD 100 can be prevented.

As described above, this specification discloses the followings.

(1) A projection display device including: a light modulation unit thatspatially modulates, in accordance with image data that has been input,light emitted by a light source; a projection optical system thatprojects the light that has been spatially modulated onto a projectionsurface of a vehicle; a measurement information acquisition unit thatacquires measurement information measured by an information measuringdevice; an image display control unit that performs either first displaycontrol for generating image data in accordance with informationreceived from a control unit that controls the vehicle and for inputtingthe image data to the light modulation unit or second display controlfor generating image data in accordance with the measurement informationand for inputting the image data to the light modulation unit; and awarning determination unit that determines, in accordance with themeasurement information, whether or not a warning is necessary, whereinthe image display control unit performs the second display control whenthe warning determination unit determines that the warning is necessary,and performs the first display control when the warning determinationunit determines that the warning is not necessary.

(2) The projection display device described in (1), further includingthe information measuring device.

(3) The projection display device described in (1), wherein theinformation measuring device is at least one selected from among anacceleration sensor, an angular rate sensor, a speedometer, an imagingdevice, a laser radar, an ultrasonic radar, and a millimeter-wave radar.

(4) The projection display device described in (2), wherein theinformation measuring device is at least one of an acceleration sensoror an angular rate sensor.

(5) The projection display device described in any one of (1) to (4),wherein the vehicle is settable to a first mode in which driving isperformed in accordance with an internally generated instruction or anexternally and wirelessly received instruction and a second mode inwhich a person drives manually, and the image display control unitselectively performs the first display control or the second displaycontrol when the first mode is set, and performs only the first displaycontrol when the second mode is set.

(6) A display control method for a projection display device having alight modulation unit that spatially modulates, in accordance with imagedata that has been input, light emitted by a light source, and aprojection optical system that projects the light that has beenspatially modulated onto a projection surface of a vehicle, the displaycontrol method including: a measurement information acquisition step ofacquiring measurement information measured by an information measuringdevice mounted in the vehicle; an image display control step ofperforming either first display control for generating image data inaccordance with information received from a control unit that controlsthe vehicle and for inputting the image data to the light modulationunit or second display control for generating image data in accordancewith the measurement information and for inputting the image data to thelight modulation unit; and a warning determination step of determining,in accordance with the measurement information, whether or not a warningis necessary, wherein the image display control step performs the seconddisplay control when the warning determination step determines that thewarning is necessary, and performs the first display control when thewarning determination step determines that the warning is not necessary.

(7) The display control method for the projection display devicedescribed in (6), wherein the information measuring device is built inthe projection display device.

(8) The display control method for the projection display devicedescribed in (6), wherein the information measuring device is at leastone selected from among an acceleration sensor, an angular rate sensor,a speedometer, an imaging device, a laser radar, an ultrasonic radar,and a millimeter-wave radar.

(9) The display control method for the projection display devicedescribed in (7), wherein the information measuring device is at leastone of an acceleration sensor or an angular rate sensor.

(10) The display control method for the projection display devicedescribed in any one of (6) to (9), wherein the vehicle is settable to afirst mode in which driving is performed in accordance with aninternally generated instruction or an externally and wirelesslyreceived instruction and a second mode in which a person drivesmanually, and the image display control step selectively performs thefirst display control or the second display control when the first modeis set, and performs only the first display control when the second modeis set.

(11) A display control program for a projection display device having alight modulation unit that spatially modulates, in accordance with imagedata that has been input, light emitted by a light source, and aprojection optical system that projects the light that has beenspatially modulated onto a projection surface of a vehicle, the displaycontrol program causing a computer to execute: a measurement informationacquisition step of acquiring measurement information measured by aninformation measuring device mounted in the vehicle; an image displaycontrol step of performing either first display control for generatingimage data in accordance with information received from a control unitthat controls the vehicle and for inputting the image data to the lightmodulation unit or second display control for generating image data inaccordance with the measurement information and for inputting the imagedata to the light modulation unit; and a warning determination step ofdetermining, in accordance with the measurement information, whether ornot a warning is necessary, wherein the image display control stepperforms the second display control when the warning determination stepdetermines that the warning is necessary, and performs the first displaycontrol when the warning determination step determines that the warningis not necessary.

(12) A projection display device including: a light modulation unit thatspatially modulates, in accordance with image data that has been input,light emitted by a light source; a projection optical system thatprojects the light that has been spatially modulated onto a projectionsurface of a vehicle; a measurement information acquisition unit thatacquires measurement information measured by an information measuringdevice; an image display control unit that performs either first displaycontrol for generating image data in accordance with informationreceived from a control unit that controls the vehicle and for inputtingthe image data to the light modulation unit or second display controlfor generating image data in accordance with the measurement informationand for inputting the image data to the light modulation unit; and aprocessor functioning as a warning determination unit that determines,in accordance with the measurement information, whether or not a warningis necessary, wherein the image display control unit performs the seconddisplay control when the warning determination unit determines that thewarning is necessary, and performs the first display control when thewarning determination unit determines that the warning is not necessary.

According to the present invention, safe driving of a vehicle can beassisted while preventing a delay in displaying important information.

The present invention has been described above based on a specificembodiment. The present invention is not limited to this embodiment, andvarious changes are possible without deviating from the technical spiritof the disclosed invention.

The present application is based on Japanese Patent Application(JP2016-181516) filed on Sep. 16, 2016, the entire content of which isincorporated herein.

REFERENCE SIGNS LIST

100 HUD

1 front windshield

2 projection surface

3 dashboard

4 control unit

5 diffusion member

6 reflection mirror

7 concave mirror

8 rearview mirror

9 imaging device

10 automobile

40 light source unit

40A light source control unit

41 r R light source

41 g G light source

41 b B light source

42 r, 42 g, 42 b collimator lens

43 dichroic prism

44 light modulation element

45 driving unit

50 motion sensor

60 system control unit

61 measurement information acquisition unit

62 warning determination unit

63 image display control unit

70 control unit

71 steering control unit

72 acceleration/deceleration control unit

73 display unit

74 navigation device

75 engine control unit

76 motion sensor

77 radar

81, 82, 83 image

What is claimed is:
 1. A projection display device comprising: a lightmodulation unit that spatially modulates, in accordance with image datathat has been input, light emitted by a light source; a projectionoptical system that projects the light that has been spatially modulatedonto a projection surface of a vehicle; a measurement informationacquisition unit that acquires measurement information measured by aninformation measuring device; an image display control unit thatperforms either first display control for generating image data inaccordance with information received from a control unit that controlsthe vehicle and for inputting the image data to the light modulationunit or second display control for generating image data in accordancewith the measurement information and for inputting the image data to thelight modulation unit; and a warning determination unit that determines,in accordance with the measurement information, whether or not a warningis necessary, wherein the image display control unit performs the seconddisplay control when the warning determination unit determines that thewarning is necessary, and performs the first display control when thewarning determination unit determines that the warning is not necessary.2. The projection display device according to claim 1, furthercomprising the information measuring device.
 3. The projection displaydevice according to claim 1, wherein the information measuring device isat least one selected from among an acceleration sensor, an angular ratesensor, a speedometer, an imaging device, a laser radar, an ultrasonicradar, and a millimeter-wave radar.
 4. The projection display deviceaccording to claim 2, wherein the information measuring device is atleast one of an acceleration sensor or an angular rate sensor.
 5. Theprojection display device according to claim 1, wherein the vehicle issettable to a first mode in which driving of the vehicle is performed inaccordance with an internally generated instruction or an externally andwirelessly received instruction and a second mode in which a persondrives the vehicle manually, and the image display control unitselectively performs the first display control or the second displaycontrol when the first mode is set, and performs only the first displaycontrol when the second mode is set.
 6. The projection display deviceaccording to claim 2, wherein the vehicle is settable to a first mode inwhich driving of the vehicle is performed in accordance with aninternally generated instruction or an externally and wirelesslyreceived instruction and a second mode in which a person drives thevehicle manually, and the image display control unit selectivelyperforms the first display control or the second display control whenthe first mode is set, and performs only the first display control whenthe second mode is set.
 7. The projection display device according toclaim 3, wherein the vehicle is settable to a first mode in whichdriving of the vehicle is performed in accordance with an internallygenerated instruction or an externally and wirelessly receivedinstruction and a second mode in which a person drives the vehiclemanually, and the image display control unit selectively performs thefirst display control or the second display control when the first modeis set, and performs only the first display control when the second modeis set.
 8. The projection display device according to claim 4, whereinthe vehicle is settable to a first mode in which driving of the vehicleis performed in accordance with an internally generated instruction oran externally and wirelessly received instruction and a second mode inwhich a person drives the vehicle manually, and the image displaycontrol unit selectively performs the first display control or thesecond display control when the first mode is set, and performs only thefirst display control when the second mode is set.
 9. A display controlmethod for a projection display device comprising a light modulationunit that spatially modulates, in accordance with image data that hasbeen input, light emitted by a light source, and a projection opticalsystem that projects the light that has been spatially modulated onto aprojection surface of a vehicle, the display control method comprising:a measurement information acquisition step of acquiring measurementinformation measured by an information measuring device mounted in thevehicle; an image display control step of performing either firstdisplay control for generating image data in accordance with informationreceived from a control unit that controls the vehicle and for inputtingthe image data to the light modulation unit or second display controlfor generating image data in accordance with the measurement informationand for inputting the image data to the light modulation unit; and awarning determination step of determining, in accordance with themeasurement information, whether or not a warning is necessary, whereinthe image display control step performs the second display control whenthe warning determination step determines that the warning is necessary,and performs the first display control when the warning determinationstep determines that the warning is not necessary.
 10. The displaycontrol method for the projection display device according to claim 9,wherein the information measuring device is built in the projectiondisplay device.
 11. The display control method for the projectiondisplay device according to claim 9, wherein the information measuringdevice is at least one selected from among an acceleration sensor, anangular rate sensor, a speedometer, an imaging device, a laser radar, anultrasonic radar, and a millimeter-wave radar.
 12. The display controlmethod for the projection display device according to claim 10, whereinthe information measuring device is at least one of an accelerationsensor or an angular rate sensor.
 13. The display control method for theprojection display device according to claim 9, wherein the vehicle issettable to a first mode in which driving is performed in accordancewith an internally generated instruction or an externally and wirelesslyreceived instruction and a second mode in which a person drivesmanually, and the image display control step selectively performs thefirst display control or the second display control when the first modeis set, and performs only the first display control when the second modeis set.
 14. The display control method for the projection display deviceaccording to claim 10, wherein the vehicle is settable to a first modein which driving is performed in accordance with an internally generatedinstruction or an externally and wirelessly received instruction and asecond mode in which a person drives manually, and the image displaycontrol step selectively performs the first display control or thesecond display control when the first mode is set, and performs only thefirst display control when the second mode is set.
 15. The displaycontrol method for the projection display device according to claim 11,wherein the vehicle is settable to a first mode in which driving isperformed in accordance with an internally generated instruction or anexternally and wirelessly received instruction and a second mode inwhich a person drives manually, and the image display control stepselectively performs the first display control or the second displaycontrol when the first mode is set, and performs only the first displaycontrol when the second mode is set.
 16. The display control method forthe projection display device according to claim 12, wherein the vehicleis settable to a first mode in which driving is performed in accordancewith an internally generated instruction or an externally and wirelesslyreceived instruction and a second mode in which a person drivesmanually, and the image display control step selectively performs thefirst display control or the second display control when the first modeis set, and performs only the first display control when the second modeis set.
 17. A computer readable medium storing a display control programfor a projection display device having a light modulation unit thatspatially modulates, in accordance with image data that has been input,light emitted by a light source, and a projection optical system thatprojects the light that has been spatially modulated onto a projectionsurface of a vehicle, the display control program causing a computer toexecute: a measurement information acquisition step of acquiringmeasurement information measured by an information measuring devicemounted in the vehicle; an image display control step of performingeither first display control for generating image data in accordancewith information received from a control unit that controls the vehicleand for inputting the image data to the light modulation unit or seconddisplay control for generating image data in accordance with themeasurement information and for inputting the image data to the lightmodulation unit; and a warning determination step of determining, inaccordance with the measurement information, whether or not a warning isnecessary, wherein the image display control step performs the seconddisplay control when the warning determination step determines that thewarning is necessary, and performs the first display control when thewarning determination step determines that the warning is not necessary.